1. Field of the Invention
This invention relates to a data disc on which text data such as a dictionary or an encyclopedia are recorded, and a method for retrieving text data recorded on the data disc by retrieving retrieval item data on the basis of index data recorded on the data disc and retrieving the text data associated with the retrieval item data.
2. Description of the Prior Art
A so-called CD-ROM disc, which is an optical disc on which data, such as dictionary or encyclopedia data, are recorded for semi-permanent storage, and a reproducing apparatus for reproducing data recorded on the disc, are currently in use.
The CD-ROM disc means a disc in which the so-called compact disc (CD) standard as one of the digital audio disc standards is expanded and in which the data of the recording format such as that shown in FIGS. 1(a) to 1(c) are recorded in place of the CD audio data. When recording data on the disc is in accordance with the data recording format, data of a predetermined unit are grouped into one block, and data readout is performed with the block as a unit. The length of one block is set to 1/75 second which is the same as the block length of a subcode of the audio CD, such that there are 75 blocks in one second. Block retrieval is performed using an absolute address of the subcode as in the case of the music CD. The total volume of data that may be recorded in each block is 2352 bytes.
The mode 0 format, shown in FIG. 1(a), is used in the lead-in or lead-out or as a demarcation of recording areas, and is constituted by a 12-byte sync signal 201, of a 4-byte header 202 and a data area 203 composed of 2336 bytes, in all of which are entered "0."
The header 202 is composed of a block address 202a, minute-unit time data of the block 202b, second-unit time data of the block 202c, a block number 202d of the block, and a mode data 202e.
The block shown in FIG. 1(b) is a block for recording data in need of operational reliability, such as character or letter data or computer data, and is constituted by sync signal 201, header 202, a 2048-byte user data area for recording desired data, error detection code (EDC), an all "0" space area 207 and a 276-byte error correction code area (ECC) 208. The ECC 208 is constituted by a 172-byte P parity 208a and a 104-byte Q parity 208b.
A block shown in FIG. 1(c) is a block used for recording data that may be corrected by interpolation even when in error, and is composed of sync signal area 201, header area 202 and 2336-byte user data area 210. User data may be entered in header 202 et seq. of this block which is not provided with a supplemental error correction code.
For retrieving the data recorded in accordance with the above described CD-ROM format, it is necessary that the logical format for record data be prescribed and the standard of the International Standards Organization (ISO) 9660 has been known as one of such logical standards.
The ISO 9660 standard prescribes the logical format shown in FIG. 2. In a predetermined absolute address on the CD-ROM disc, that is, in a 2 second 16 sector position, a volume description 211 is recorded. In this volume descriptor 211, there are recorded the manner in which the disc is logically organized, route directory position data for a standard file system structure, recording on copyright data, the file name and publishing company.
In the route directory 212 stored in the address indicated by the route directory position data, there are recorded, for example, the positions and lengths of the files 213 recorded in the data disc.
These files 213 are a plurality of literatures or publications recorded on the data disc, such as Japanese language dictionary, English-Japanese dictionary, Japanese-English dictionary or the Chinese-Japanese dictionary.
The recording format of a file 213 is the last that is prescribed in the ISO 9660 world standard. Thus, it is up to the data disc publisher to record main text data downstream of the file 213 in an optional format and to develop by its own efforts the method of retrieving the main text data recorded by this optional format.
The method for retrieving the main text data is written into, for example, a floppy disc or an IC card, and is formulated as the data retrieving software.
It is up to the user to purchase the data-retrieving software with the data disc and to operate the reproducing equipment in accordance with the retrieving method uniquely developed by the data disc publisher to retrieve the desired data.
With the above described ISO 9660 world standard, the recording format for file 213 is the last that is prescribed, and main text data, for example, downstream of the file 213, has to be recorded by a desired format by each data disc publisher and the method for retrieving the main text data recorded by such optional format is uniquely developed by the publisher. The result is that the data retrieving method differs from one data disc publisher to another so that production costs become prohibitive due to increased time and expenses for developing the retrieving methods.
Since the retrieving method differs from one data disc to another, the user is obliged to learn the retrieving method for each data disc and to purchase the retrieving software for each data disc at considerable expense. This is not desirable for versatility of the data discs and reproducing equipment for the data disc.
Besides, since the retrieving software needs to be written in other media, such as floppy discs or IC cards, driving systems for the data disc and the retrieving software become necessary with the result that the reproducing equipment becomes bulky in size to render it difficult to cope with the recent tendency towards smaller sized equipment.
Although there is known a retrieving method for retrieving plural data discs for dictionary type data by a sole type of the retrieving software, this retrieving method also is not practically useful since the discs are limited to those for dictionary type data.